1. Field of the Invention
This invention relates to determining range in three-dimensional imaging systems.
2. Background Information
Laser techniques, such as LADAR (Laser Detection and Ranging) or “LIDAR” (Light Detection and Ranging), are currently being used to image objects in three-dimensional image systems. Light, often from a laser source, is directed toward an object of interest. Reflected light from the object is then gathered and focused on one or more photodetectors.
LADAR systems are capable of determining the distance to an object, for example, by timing the travel time of light pulses sent round trip from a source to the object and back to a detector. However, adapting such systems to image remote objects challenges the sensitivity and speed of available devices.
Stettner et al, in U.S. Pat. No. 5,446,529 (1995), describes an array of detectors placed at the image plane to detect a two-dimensional image frame, which can be further processed to enhance the image. If adequate light is gathered and the reflective emissions of the object are distinguishable from noise, an object can be identified by such a system.
In some laser imaging systems either the scanner or the receiver is scanned across the object, and multiple laser pulses are used to probe the contours of the object. An example of such an approach is shown in U.S. Pat. No. 6,734,849, issued to Dimsdale et al. on May 11, 2004.
In U.S. Pat. No. 5,892,575 (1999), Marino, on the other hand, discloses a system for imaging a scene using an array of monolithic light detectors operating in non-linear Geiger mode. In one “scanner-less” embodiment disclosed by the patent, a processor develops an image of the target scene based on the round trip travel times of object-reflected photons received by a photodetector array at multiple positions on the array.
The approaches to date have been complex and, therefore, expensive to produce and maintain. What is needed is a system and method for imaging which addresses the above issues and other issues that will become evident when reading the description below.